V Oz to JNB
I don't know how V Oz is expecting to operate SYD to JNB. The performance and max uplift from JNB will be quite limited due to the airport elevation of 5558ft.
The numbers I come up with are about 302.8t T/O weight. (this is using 30C, QNH 1013 and nil wind on Rwy 03L). With 15degrees its 318.8t.
Probably not going to work very well for a least half of the year due to high temperature alone.